This research is in progress. The hippocampus is crucial for memory formation. New neurons are added throughout life to the hippocampal dentate gyrus (DG), a brain area considered important for differential storage of similar experiences and contexts. To better understand the functional contribution of adult neurogenesis to pattern separation processes, we used a novel synapse specific trans-neuronal tracing approach to identify the (sub) cortical inputs to new dentate granule cells (GCs). It was observed that newly born neurons receive sequential innervation from structures important for memory function. Initially,septal-hippocampal cells provide input to new neurons, including transient innervation from mature GCs as well as direct feedback from area CA3 pyramidal neurons. After about 1 month perirhinal and lateral entorhinal cortex, brain areas deemed relevant to integration of novel sensory and environmental information, become substantial input to new GCs. The proposed functional relevance of new neurons, can now be examined within the context of their unique neural circuitry and it will be determined how this circuitry is modified by exercise..